Refining nickel



Patented all".v l9, i946 a STATES REFINING NI William J. Kroll,NiaFails, N. Y.

No Drawing. Application 22, 1944,

. Serial No. 527,865

12 Claims. (or. 15-82) This invention relates to metallurgical proc=esses and more particularly to a process for refining nickelcontaminated with metallic impurities to remove the metallic impuritiestherefrom.

Heretofore in the art, the preparation of substantially pure nickel ornickel containing relatively small amounts of metallic impurities hasbeen exceedingly difiicult and has required the practice of complicatedand costly processes.

The object of the present invention is to provide a process for theelimination of associated metal impurities from metallic nickel. I

Another object is to provide a process for discovered that, contrary toexpectations based molten metal chloride fusions.

As a resultof this discovery I have devised an improved method oftreating impure nickel to eliminate therefrom substantially anassociated metal impurities which consists essentially in reducing orcomminutlng the impure nickel to fine particle size and suspending ordispersing the same in a fused metal chloride bath containing nickelchloride for and extended time interval adapted to efiect or obtain aremoval of the said associated metallic impuritiesby a displacementreaction between the said impurities and the nickel chloride, thenseparating the metal from the i'used bath.

There are many diflerent ways in which the present invention may beadapted in the art of purifying nickel of its associated metallicimpuri-.

ties and of introducing the invention as an essential step in a processof recovering nickel from its ores. I will describe, first, the basicprinciples involved in the displacement reaction and, secondly, whereinthis basic reaction may be adapted in the treatment of impure nickelmetal powder in the elimination of certain heavy metal impurities and inthe treatment 01 nickel scrap materials to eliminate therefromassociated metal impurities.

The basic displacement reaction of the present 7 invention iscomplicated, to a certain extent by alloy and intermetallic compoundformation between the nickel and the displacing metal and by therelative rates of difilusion of the two metals into and through eachother. To overcome this complication and to reduce the same to a loworder, it is essential to reduce the nickel to a a small particle sizeor thin section thereby toreduce the diflusion path to the smallestdistance that'is economically practical to obtain.

The reaction involved is essentially one of displacement according toone or more of the reactions below indicated;

(eta) This reaction will occur at all temperatures at which the Nifilzand the resultant chloride compound or the displacing metal may be maintained in a liquid anhydrous phase but the rate of the reactionincreases markedly with increase in temperature and is most rapid attemperatures above about 700 C. and below the boiling point of thechloride compound of the displacing metal when boiling point lies belowthat of nickel chloride (975 CJ.

I have found, however, that by melting nickel chloride in a metalchloride fusion consisting principally of one or more of the chloridecompounds of the most stable metal chlorides, such as the alkali andalline earth metal chlorides, a wide range of liquid anhydrous metalchloride fusion mixtures may be obtained that are highly stable and antto omdation decomposition when heated in the open air to temperatures ashigh as 975 C. to 1000 C. and which are operative in accordance with thepresent invention at temperatures as low as 500 C. a

In general, though, I prefer to employ a metal chloride, fusion mixtureconsisting of potassium and sodium chlorides mixed in the ratio of 60%KC! and 40% NaCl and having a melting point of 650 C. To any givenvolume or this fusion mix I add N101: in the total amount desiredrelative to the associated metal impurities of the comminuted nickeldispersed therein, usually adding the said nickel chloride in suchincrements as may be necessary to maintain a large excess of NiClzv overthat theoretically required and preferably between 25 to 50% NiClz (byweight) in the fusion mix. The addition of NiClz to this preferredfusion mixture or base chloride fusion normally lowers the melting pointto below 500 C. and temperatures as high as 1000 C. may be safelyemployed without excessive loss by volatilization of the nickelchloride.

The amount of comminuted nickel immersed and suspended in the moltenmetal chloride bath may be varied widel without essential departure fromthe present invention as one skilled in the art will recognize, and isprimarily dependent upon the total amount of impurities it is desired toeliminate in one treatment. As the displacement reaction involvedresults not only in a solutioning of the associated metal impurities butalso in an enrichment of the metallic residue with precipitated nickel,in many instances it may be only necessary to lower the percentage ofcontained associated impurities materiall to obtain an intermediatepurified nickel product containing the remaining impurities withintolerance percentages suitable, in some instances, for use in the trade.Again, it may be desired only to selectively remove one or more of theassociated impurities, it being apparent that where two or moreassociated metal impurities are present in the nickel, the one higher inthe displacement series will be dissolved out in major proportion beforesolutioning of the second impurity appreciably initiates.

In this connection, m investigations indicate the following approximatedescending order for the various metals, commonly found associated withnickel, in the displacement series of metals in molten metal chloridebaths containing nickel chloride: V, Mn, Zn, Cr, Fe, Co, Cu, Ni.

The alkali and alkaline earth metals and magnesium lie to the left ofthe list or above V and only a few metals lie to the right or below Ni.The metals A Pb, Sn, Cd, Al, Be, U, 'I'h, all he above Ni in thisdisplacement series and if present in Ni also would be removed alongwith any of the metals in the series above noted.

With respect to the above series, some of the metals form intermetalliccompounds which resist decomposition in accordance with this series. Asan example, the intermetallic compound nickel silicide is more noblethan Ni and very difflcult to break down, and in most cases the siliconcontent of nickel alloys is largely retained.

In the practice of the present invention, Iprefor to malntain'atemperature substantially below the boiling point of the chloridecompound 7 of the displacing metal, but not over the boiling point ofnickel chloride (975 to 1000 C.), and a temperature approximating 700 C.whenever practicable. However, temperatures as low as 500 C have beenemployed in the practice of the present invention with good results.

The melting and boiling points of the chloride compounds of the morecommon metal impurities are as follows:

As one specific example of the present invention, but not as alimitation thereof, nickel ture of the bath was maintained for about onehour at 650 C. at the endof which time the metal powder was separatedfrom the fusion mixture and the cobalt content remaining thereindetermined by chemical analysis. The chemical analysis showed that 70%of the cobalt content of the nickel metal powder had been removed inthis relatively short time of treatment.

By extending the time interval of treatment to two hours;-or byincreasing the amount of mm: in the fusion mixture to increase the rateof the displacement reaction; or by reducing the particle size of thenickel powder to below 200 mesh; or by repeating the above treatment,the amount ofcobalt removed from the nickel powder may be varied widely.It is not always desired to effect a substantially complete removal ofthe cobalt in one extraction treatment, except where, in addition tocobalt, the metal powder contains undesired amounts of other impuritieslower than Co in the displacement series. In that event substantiallyall of the Co must be removed before any of these other metals may beremoved.

In general, I- prefer to employ higher concentrations of MC]: in thefusion mixture of alkali metal chlorides than given in the above exampleand concentrations within the range 25-50% are preferred so as to obtainas rapid a rate of displacement as possible at an operating temperatureof 650-750 (3., thereby to materiall shorten the required time intervalof treatment. With this high concentration of N101: in the fusionmixture I find that the amount of nickel powder incorporated therein fortreatment may be greatly increased, the'precise amount of increasedepending upon the total amount of associated impurities present.

Ni in the displacement series. With Cu, for example, a large excess ofN10]: must be present in the fusion, whereas with Zn and Mn relatively asmall excess is required. By maintaining such an excess, however, from'70 to of any given metal may be removed in each treatment and byrepeating the treatment several times a sub-.

stantially complete removal may be eflected.

Where substantiall complete removal of these associated impurities onlyis desired, a second treatment using a molten flux substantially free ofthe displacing metal chloride is generally effective where the originalamount of the contaminating metal is not excessive.

As a second specific example, a metal powder passing about mesh andconsisting principally of nickel but containing copper in about the per-.centage usually present in Monel metal which powder was obtained by thehydrogen reduction of mixed Ni and Cu oxides, was suspended in a moltenbath consisting oi'a 60/40 mixture a KC! and NaCl containing about 25%nickel chloride, the mixture being about two part fusionmixture' to onepart metal powder. The bath temperature was maintained at 700 C. and thetime interval of treatment approximated one-half hour. After separatingthe metal powder from the fusion mixture. chemical analysis of the metalpowder showed that 72% of the copper had been removed in this short timeinterval of treatment. Longer time intervals of treatment have resultedin substantially complete removal (90-95%) of the copper content of thismetal powder, and a second treatment in a similar fusion mixture usually resulted in an even greater purity nickel powder product.

As another example, nickel metal powder-containing Fe as an impuritywhen added to the fusion mixture used in the above second example inabout the same relative proportions and under substantially the sametime and temperature conditions resul ed in the removal of 80% of theironwithin one-half hour and 90 to 95% of the iron at the end of anhour.

From the above examples. it is believed apparent that the removal of Co.Cu and Fe from nickel may be easily effected by the practice of thepresent invention. The metals .Al. Zn and Mn, are even more'easilyremoved in the same manner and under the same conditions. as thesemetals are higher than Cu. Co and Fe in the displacement series as herenbefore noted. In eneral. Mn. Zn and Al will be removed in higherpercentages in one treatment than is usually obtainable with Cu. Fe orC0.

The ada ta ion of the inven ion to the tr atment of nickel scrap is ofparticular im ortance in the art. i asmuch as it is known that it isextremel .diiiicult in remelting scrap nickel to eliminat therefrom manyof the metals as ociated therewi h in alloy or occluded form. S me ofthese metals may be removed in major part from the molten alloy byoxidation but some con taminating metals. such as iron and cop er, maynot be separated from nickelin thi manner.

In accordance with the present inventi n, t e scrap nickel followingreduction in particle size to pass 60 to 100 mesh in any convenientmanner,

3 to a second treatment in afresh batch of the fusion mixture undersubstantially the same conditions for another hour, thereby effecting aremoval of 90 to 95% of the associated metal impurities.

Whether ornot a third treatment is to be given forming Cu-containingnickel alloys, as an exis subjected to extended heat-treatment in a C.(the B. P. of NiClz) and as low as 500 C. without essential departurefrom the present invention, the specific temperature being selected withrespect to the impurities present to obtain t e most economicallypractical rate of displacement with consequent shortest time interval oftreatment to obtain the desired percentage of removal of impurities inthe first treatment.

In general, from to 70% of the associated metal impurities may beremoved from the nickel by means of the above fusion mixture, within atime interval of treatment approximating one hour. In general, I preferto end the treatment after one hour and after separating the metal cakefrom the fusion mixture, subject the metal ample, the refiningoperation, of course, may be terminated when copper content of thenickel is within the tolerance limits of the alloy to be formedtherefrom.

As an alternative practice a sequence of treat ments may be practiced onthe scrapnickel whereby each of the contaminating metals are selectivelyremoved.

Alternatively, also, the scrap nickel ma be melted, subjected to anoxidizing blast to remove some of the contaminating metals, cast intoingots, fragmented and comminuted to the desired particle size, and thentreated in accordance with ispreferableto break the thin sectionedchips.

and turnings into relatively small fragments before treating inaccordance with the present in- I vention regardless of section.

Various other modifications and adaptations of the present inventionwill be apparent to one skilled in the art from the above disclosure ofthe present invention but all such are contemplated asmay fall withinthe scope of the following claims.

What I claim is:

l. The method of treating a molten metal chloride bath containing nickelchloride to remove the nickel content of said bath as metallic nickelwhich comprises incorporating in said bath a finely divided metallicmaterial having a melting point above the temperature of the bath andconsisting at least in part of a metal higher than nickel in the solidmetal-molten metal chloride displacement series at the temperature ofheatins.

2. The method of treating a molten metal chloride bath containing nickelchloride heated to temperatures within the range 500-1000" C. to removethe nickel content of said bath as metallic nickel which comprisesincorporating in said bath a finely divided metallic material having amelting point above thetemperature of the bath and consisting at leastin part of a metal selected from the group of metals Al, Mn, Zn, Cr, Fe,Co, and Cu, r

3. The method of treating a molten metal chloride bath containing nickelchloride to remove a good part of the nickel content of said bath asmetallic nickel which comprises heating the bath to a temperature withinthe range 500-1000 C. and incorporating a finely divided alloy of nickeland copper in said bath the amount of the copper in said alloy beingsubstantially less than that theoretically required to displacesubstantially all of the nickel from the chloride combination.

4. The method of removing metallic impurities from nickel whichcomprises reducing the impure nickel to small particle size anddispersing the small particle sized material in a molten metal chloridebath consisting of a mixture of nickel chloride and metal chloridecompounds of metals relatively high in the displacement series inthesystem solid metal-molten metal chloride, and heating the said bath to atemperature within the range 500-1000 C. for a time interval pronickelchloride, said highly stable metal chlorides being selected to provide afusion temperature within the range 500 to 1000" C.

6. The method of removing metal impurities from metallic nickel whichcomprises reducing the impure nickel to relatively small particle sizeand suspending the small particle sized material in ,a metal chloridefusion consisting of a mixture of alkali metal chlorides and nickelchloride having a temperature within the range sou-100m '7. The methodof claim 6, wherein the amount of said nickel chloride is maintained inlarge excess of that theoretically required to remove substantially allof the said metal impurities b a displacement reaction.

8. The method of claim 6, wherein the amount of said nickel chloride ismaintained in large excess of that theoretically required to removesubstantially all of said metal impurities by a displacement reactionand wherein the time interval of treatment is limited to that effectinga removal of the major portion of said impurities within an economicallypractical short time and wherein the said treated metal is subjected toat least one other treatment in at least one more bath of said fusionmixture to obtain a removal of the greater portion of the remainingmetal impurities.

9. The method of treating metallic nickel to eliminate therefromassociated metallic impurities oi? the group consisting of Cu, C0, Fe,Cr, Zn and Mn, which comprises reducing the impure nickel to fineparticle size and suspending the said fine particle sized material in amolten metal chloride, bath containing nickel chloride and metalchlorides higher than Mn in the displacement series of solid metals infused metal chlorides at temperatures within the range 500-l000 C.

10. The method of claim 9, wherein said molten metal chloride bathconsists of a mixture of KCl 4 and NaCl.

11. The method of claim 9, wherein the amount of said nickel chloride isin large excess of the theoretical amount required to obtainsubstantially complete removal of said metal impurities by adisplacement reaction.

12. The method of claim 9, wherein the time interval of immersion insaid bath is limited to a time interval providing for the removal of themajor proportion of said metal impurities within a relatively short timeinterval and wherein the metal is given further treatments in newbatches of said fusion mixture to remove the major portion of theremaining impurities.

WILLIAM J. KROLL.

